Hm, remember the great RASTER plugin Access Denied did? This is a bit off topic of how to create a Line Art. But there is an idea of how to create hatch-Art. What if there as a hatch option, which draws horizontal and vertical lines in a grid (with a bit of random) all over the picture, and just change the thickness of the lines thicker and thinner depending on the background color of the image? It could look like hatch-vector art...

BTW, I would have paid for the RASTER plugin, as I'm sure it was alot of work.